In the oil and gas industry, hydraulic fracturing involves injecting fracturing fluid through a wellbore and into a formation under sufficiently high pressure to create fractures, thereby providing channels through which formation fluids such as oil, gas or water, can flow into the wellbore and thereafter be withdrawn. Fracturing fluids are designed to enable the initiation or extension of fractures and the simultaneous transport of suspended proppant (for example, naturally-occurring sand grains, resin-coated sand, sintered bauxite, glass beads, ultra lightweight polymer beads and the like) into the fracture to keep the fracture open when the pressure is released.
Water or hydrocarbons have been commonly used as base fluids for fracturing. While usually effective, water based fluids can be harmful to certain types of formations, and are not effective at removing excess water from a well (removing “water blocks”). The recovery and retention of the injected aqueous fluids have proven to be important parameters affecting the productivity of the pay zone. Insufficient recovery of injected aqueous fluid may significantly lower the productivity.
Therefore, it has been suggested to use chemical additives to optimize clean-up and recovery of aqueous fracturing fluids. Flowback aids are usually surfactants or cosolvents added to stimulation treatment fluids to reduce capillary pressure and remove water blocks. As the stimulation of tight gas reservoirs is becoming more important, the perceived value of these additives has grown. The flowback aid benefits production by reducing damage due to phase trapping, enhance mobilization of the oil and gas, help to increase regained permeability, and improve oil/gas recovery.
Historically, fluorosurfactants have provided a good combination of surface tension reduction and fluid recovery (L. Kalfayan, B. Haley, and Weiss “Optimizing surfactants to improve stimulation flowback in tight gas wells”, World Oil, Nov. 1, 2008). However, environmental concerns about fluorosurfactants and their potential degradation products led to the search for alternatives.
Glen Penny and John T. Pursly “Field studies of drilling and completion fluids to minimize damage and enhance gas production in unconventional reservoirs”, Socienty of Petroleum Engineers, SPE 107844-MS, 2007 disclose the use of nonionic alcohol ethoxylates, nonylphenol ethoxylates, mixtures of methanol and fluorosurfactants and of microemulsions for drilling and completion fluids but also for fracturing processes.
Paul R. Howard, Sumitra Mukhopadhyay, Nita Moniaga, Laura Schafer, Glen Penny, and Keith Dismuke “Comparison of Flowback Aids Understanding their capillary pressure and wetting properties”, Socienty of Petroleum Engineers, SPE 122307-MS, 2009 disclose the use of linear ethoxylated alkohols, micoemulsions, amine oxides, and isoalkylalcohols as flowback aids.
P. Kaufman et al. “Critical Evaluations of Additives Used in Shale Slickwater Fracs”; Society of Petroleum Engineers, SPE 119900, SPE Shale Gas Production Conference, Irving, Tex. disclose ethoxylated n-decanol, a microemulsion, nonyl phenol ethoxylated and ethoxylated fluorosurfactants for shale treatment to lower surface tension.
K. E. Cawiezel, A. K. Singh, P. S. Carman, J. L. Cutler, “The Selection and Optimization of a Surfactant Package to Maximize Cleanup of a High-Density Fracturing Fluid” in SPE 136812-MS 2010, SPE Deepwater Drilling and Completions Conference, Galveston, Tex. disclose test methods for the selection of surfactants for recovering fracturing fluids. The paper also discloses results for several surfactants but does not disclose any details about the chemistry of such surfactants.
Mohan K. R. Pangs, I. Suzylawati, P. Cheneviere, and M. Samuel “Preventive Treatment for Enhancing Water Removal from Gas Reservoirs by Wettability Alteration” disclose the use of several chemicals for the improvement of the removal of water blocks in gas reservoirs. Besides fluorine based surfactants and polymers no details about the chemicals tested are provided.
PCT patent application PCT/EP2013/059947 discloses the use of esters of alkoxylated saccharides having esters groups comprising hydrocarbon residues having from 6 to 30 carbon atoms as wettability modifiers. It also mentions the use of such components in fracturing operations for improving the penetration of an aqueous fracturing fluid into the formation, however, the application does not disclose the use of said alkoxylated saccharides as flowback agents.
US 2011/0218126 A1 discloses an environmentally, green, non-toxic composition comprising besides water at least 4 different components, namely (a) water soluble esters of low molecular weight alcohols and of low molecular organic acids, (b) oil soluble esters of low molecular weight alcohols and of high molecular weight fatty acids, (c) water soluble non-ionic surfactants from vegetable or animal sources, and (d) amphoteric surfactants derived from animal or vegetable based sources. Examples for (c) include ethoxylated and/or propoxylated alcohols such as lauryl alcohol, stearyl alcohol, oleyl alcohol or polyglucosides.
It is known in the art to use alkyl polyglucosides for oilfield applications (as disclosed for example in WO 2006/026732 A1, WO 2007/063069 A2 or WO 2011/038745 A1), however it has not yet been known to use them as flowback aids in fracturing operations.
There is still a need for fracturing processes with improved flowback performance in which environmentally acceptable surfactants may be used.